Add a comment about cache coherency and retranslation, so that people
developping new targets based on existing ones are warned of the issue.
Cc: Alexander Graf <ag...@suse.de>
Cc: Edgar E. Iglesias <edgar.igles...@gmail.com>
Signed-off-by: Aurelien Jarno <aurel...@aurel32.net>
---
tcg/arm/tcg-target.c | 3 +++
tcg/ia64/tcg-target.c | 3 +++
tcg/mips/tcg-target.c | 4 +++-
3 files changed, 9 insertions(+), 1 deletions(-)
diff --git a/tcg/arm/tcg-target.c b/tcg/arm/tcg-target.c
index 1eb5605..918e2f7 100644
--- a/tcg/arm/tcg-target.c
+++ b/tcg/arm/tcg-target.c
@@ -352,6 +352,9 @@ static inline void tcg_out_b(TCGContext *s, int cond,
int32_t offset)
static inline void tcg_out_b_noaddr(TCGContext *s, int cond)
{
+ /* We pay attention here to not modify the branch target by skipping
+ the corresponding bytes. This ensure that caches and memory are
+ kept coherent during retranslation. */
#ifdef HOST_WORDS_BIGENDIAN
tcg_out8(s, (cond << 4) | 0x0a);
s->code_ptr += 3;
diff --git a/tcg/ia64/tcg-target.c b/tcg/ia64/tcg-target.c
index e2e44f7..8dac7f7 100644
--- a/tcg/ia64/tcg-target.c
+++ b/tcg/ia64/tcg-target.c
@@ -871,6 +871,9 @@ static void tcg_out_br(TCGContext *s, int label_index)
{
TCGLabel *l = &s->labels[label_index];
+ /* We pay attention here to not modify the branch target by reading
+ the existing value and using it again. This ensure that caches and
+ memory are kept coherent during retranslation. */
tcg_out_bundle(s, mmB,
tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0),
tcg_opc_m48(TCG_REG_P0, OPC_NOP_M48, 0),
diff --git a/tcg/mips/tcg-target.c b/tcg/mips/tcg-target.c
index 4e92a50..e04b0dc 100644
--- a/tcg/mips/tcg-target.c
+++ b/tcg/mips/tcg-target.c
@@ -351,7 +351,9 @@ static inline void tcg_out_opc_imm(TCGContext *s, int opc,
int rt, int rs, int i
*/
static inline void tcg_out_opc_br(TCGContext *s, int opc, int rt, int rs)
{
- /* We need to keep the offset unchanged for retranslation */
+ /* We pay attention here to not modify the branch target by reading
+ the existing value and using it again. This ensure that caches and
+ memory are kept coherent during retranslation. */
uint16_t offset = (uint16_t)(*(uint32_t *) s->code_ptr);
tcg_out_opc_imm(s, opc, rt, rs, offset);
--
1.7.2.3
